Rolling includes rolling of a steel material and rolling of nonferrous metal material, such as aluminum or copper. Moreover, there is a difference in shape, such as rolling of a plate material or rolling of a bar material. Moreover, examples include hot rolling or plate rolling that rolls a material by heating thereof to high temperature and cold rolling that rolls a material of room temperature. Materials are separately formed in accordance with particular uses or purposes.
In any type of rolling, a material is put between rolling rolls to cause it to be thin or long and narrow. Therefore, as a power source for driving the rolling rolls, a motor is commonly used.
A general configuration of a rolling mill will be described. The rolling mill includes a pair of parallel rolling rolls for rolling a material. Each of the rolling rolls includes a spindle, which is a rotation shaft. Moreover, the rolling mill includes a motor. The motor includes a motor rotation shaft. The spindle and the motor rotation shaft are connected via a gear mechanism, and thereby power of the motor is transmitted to the spindle. Moreover, to the motor rotation shaft, a motor speed sensor for detecting the speed thereof is attached.
In such a configuration, the speed of the motor is controlled based on a comparison value between an actual value of the speed detected by the motor speed sensor and a target value of the motor speed so that the actual value and the target value coincide with each other.
Note that the applicant recognizes the following literatures as being related to the present invention.